Terrestrial broadcast services for small mobile devices with small antennas, e.g. Mobile TV and other multimedia services, is an area that has gained a lot of attention. For example, Multimedia Broadcast and Muilticast Services (MBMS) have been defined and developed for GSM and WCDMA mobile systems, as well as for CDMA2000 systems.
One such system is the Universal Mobile Telecommunication System (UMTS). UMTS employs a Universal Terrestrial Radio Access Network (UTRAN), consisting of a set of Radio Network Subsystems (RNS) connected to a Core Network through an interface (the Iu interface). Each Radio Network Subsystem usually includes a plurality of radio base stations (Node Bs) connected to an RNS specific Radio Network Controller (RNC) through the Iub interface. This is illustrated in FIG. 1.
In UTRAN, the radio resource for a radio link in one cell (one Node B may support a plurality of cells, e.g., 3, 6, 9) is defined by a chammelisation code. When a radio link is set up between a UE and a Node B, this code is selected by the RNC.
The increasing communication resource demands, however, has resulted in development of even newer technologies, and the UMTS system is expected to evolve into a high speed Orthogonal Frequency Division Multiple Access (OFDMA) system, in 3GPP currently denoted Long Term Evolution (LTE). MBMS services in LTE are presently called evolved MBMS, or eMBMS.
Similar to UMTS, multimedia broadcast and/or multicast transmissions in LTE may be transmitted in a single cell or in a group of cells. In case of multi-cell transmission, however, LTE differs from CDMA systems in that Single Frequency Network (SFN) operation mode is assumed for these transmissions, i.e. the transmission is synchronized in such a way that the UE may combine the energy from multiple transmissions from different cells without additional receiver complexity. SFN transmission is possible if identical information is transmitted from different cells in “the same” physical radio resource at the same time using the same coding scheme. In OFDMA, which, as stated above, is used in LTE, a physical radio resource is defined by a set of frequencies and a time slot.
Accordingly, mobility in an SFN network is seamless without explicit handovers. SFN transmissions, however, suffer from a more complicated communication resource allocation as result since the allocations in an SFN service area must correspond in frequency and time.
Although UMTS UTRAN employs macro diversity for voice calls, i.e., the UE is connected to more than one Node B and the same information is transmitted and received by these Node Bs, this voice call information is encoded differently since every UMTS node B employs a Node B-unique scrambling code on all transmissions. The UE must therefore assign different receiver resources for each Node B to be able to decode signals from two or more Node Bs. When employing broadcast and/or multicast services such as mobile TV in the UMTS system, the broadcast transmission will be transmitted from different Node Bs using Node B unique scrambling codes, however, there is no combination of transmissions from different cells.
The introduction of MBMS, denominated evolved MBMS or eMBMS in LTE, thus has introduced additional communication resource allocation issues when introducing SFN transmissions.
This allocation is further complicated by the architecture of LTE, since in LTE there is no central node (RNC) controlling multiple Node Bs. Instead, in LTE, the functionality for selecting physical radio resources is located at the Node B. Further, the system may be arranged so that different service providers may independently initiate broadcast and/or multicast transmissions in the same or partially overlapping portions of the radio access network. For example, the radio access network may be divided into overlapping service areas, which are configured by O&M and used to select which service shall be available in a certain area. For example, service area “Stockholm Globe Arena” would be overlapping with service areas “Stockholm” and “Major Swedish Cities”. Furthermore, Service Areas being smaller than the possible SFN area could be expected to be a common case, e.g., at sports events, covering airports, train stations, etc.
Consequently, the probability that at least part of resources requested for a SFN transmission are already occupied in one or more of the requested Node Bs, or radio transmitters of a single Node B, may be quite great, in particular when considering a rather large coverage area. If the resource is occupied, the resource activation would fail in those Node Bs and must be performed again for all the Node Bs in the area. Consequently, the resource allocation may be time consuming.
Accordingly, there exists a need for a more efficient method for allocating communication resources in a terrestrial wireless communication system, in particular for SFN transmissions.